1. Field of the Invention
The present invention relates to a method of manufacturing a carbon nanotube device in which carbon nanotubes (hereinafter referred to as CNTs) are used for a channel forming region formed between a source electrode and a drain electrode, and more particularly to a method of manufacturing a CNT semiconductor device in which an alignment direction of the CNTs is controlled and the source electrode and the drain electrode are electrically connected with each other.
2. Description of the Related Art
In recent years, a CNT has been discovered and remarked as a new carbon material different from graphite, amorphous carbon, and diamond that had been known until then. The reason is that the CNT exhibits specific electronic physical properties different from those of existing carbon materials.
The CNT is a material with a cylindrical shape obtained by rolling up a layer of graphite in which six-membered rings of carbon are linked (graphene sheet). A diameter of the CNT is about 1 nm to several tens nm and a length thereof is about 1 μm. In addition, the CNT is classified into a single-walled CNT (SWCNT) including only a single layer and a multi-walled CNT (MWCNT) in which multiple layers are formed in a concentric cylindrical shape. With respect to the CNT, the MWCNT was first discovered in 1991 by Iijima, NEC (Nippon Electronic Corporation), and next, the SWCNT was simultaneously reported by the NEC group and the IBM group in 1993.
Also, with respect to specific properties of the CNT, there are, for example, (1) a shape (tip diameter is small and an aspect ratio is large), (2) electronic physical properties (there are a CNT with a semiconductor property and a CNT with a metal (conductor) property according to how to roll up a graphene sheet and a diameter of the rolled up sheet), (3) an absorption property, and (4) a superior mechanical property. Various attempts using these properties have been made.
Further, in a technique related to the CNT, development of probes which can be applied to a scanning probe microscope (SPM) is on the way. Note that the CNTs dissolved in a solvent are present as in a tangled thread in a solution at random. Therefore, according to the technique, the solution is dropped onto an electrode, an alternating current voltage is applied thereto, and the CNTs are subjected to electrophoresis in the solution. After that, the solvent is removed from the solution to deposit the CNTs having a strong anisotropy near the electrode. The thus obtained needle-like CNT is utilized as a cartridge of a probe of the SPM (Y. Nakayama, et al., J. Vac. Sci. Technol., B18, p. 661 (2000)).
Now, a size of a silicon device as a current dominant electronic device is reduced with the progress of a high level microfabrication technique so that a width of the gate electrode of a field effect transistor (FET) is as small as about 0.1 μm. However, when a further high level microfabrication is conducted, there are many problems in a fabrication process such as an exposure technique and the microfabrication is approaching its limit.
Therefore, a nanometer-sized device using CNTs having a property so as to become a conductor or a semiconductor depending on a slight change in the manner of atomic arrangement (chirality) has been expected.
A report related to a field effect transistor (FET) using a CNT has been made already and such a transistor is called a TUBEFET. FIG. 6 shows a typical structure of a TUBEFET. As shown in FIG. 6, an oxide film (150 nm to 300 nm) as a gate insulating film 602 is formed on a silicon substrate 601 which becomes the gate, a source electrode 603 and a drain electrode 604 containing gold or platinum are formed thereon, CNTs diluted with an organic solvent and dispersed are applied, and the TUBEFET is formed using a CNT 605 bridged between the electrodes with a preferable state. However, because the TUBEFET cannot be produced by separately manipulating the CNTs, the control of those becomes one of the problems to practical use.
As described above, in the case where the nanometer-sized device is manufactured using the semiconductor property of the CNT, if the CNT is not provided at a desirable position (more specifically, a position at which the conductors (electrodes) constituting the device are electrically connected with each other), such a structure does not function as the device. However, the structure is minute and a generally used CNT solution is present so as to tangle the CNTs in a solvent. Therefore, it is very difficult to provide the CNT at a necessary position.